The subject matter disclosed herein relates to magnetic resonance including nuclear magnetic resonance and electron magnetic resonance. Spin polarization is important to magnetic resonance and thus to analytical science. Some strategies of ‘dynamic’ polarization of nuclear spins have been introduced in the past. However, they either work at very low temperatures (10K and below) or are incapable of generating polarization superior to that obtained with the use of a strong magnet. Despite these limitations, higher spin polarization is in such high demand that several companies have developed complex (and very expensive) instruments that partly overcome these problems. Here the sample is previously cooled down to about 10K or below, hyperpolarized, thawed and then quickly transferred to the high-field magnet in the form of a polarized fluid. Such systems are not only pricey but also expensive to operate. Most existing technologies for nuclear spin polarization enhancement belong to one of the categories identified below.
Dynamic nuclear polarization via the Overhauser effect: In this case a radical (i.e., a molecule containing unpaired electron spins) is dissolved in the target fluid. A continuous radio-frequency (or microwave) field is applied at the electronic Zeeman frequency of the radical. The enhancement is proportional to the thermal polarization of the unperturbed nuclear system (i.e., grows with the applied magnetic field) and reaches up to 600 times (in practice, the enhancement typically reaches less than 200 times). Because the technique only works at relatively low fields (up to 0.1-0.3 T), similar polarization can be attained by simply immersing the sample in a superconducting NMR magnet (10 to 20 T).
Optical pumping of semiconductors: This technique uses laser light to generate polarized photoelectrons, which can then transfer the polarization to nuclei upon recombination. This technique exploits very specific optical selection rules found in semiconductors. It has been shown that this polarization can, in principle, be transferred to solid organic films deposited on top of the semiconductor material. Unfortunately, the technique exclusively works at very low temperatures (below 10K) and thus finds reduced applicability.
Contact with hyperpolarized xenon (or other noble gases): In this case, xenon gas is first polarized by contact with optically pumped Rubidium vapor (or some other alkaline vapor). To produce pure hyperpolarized Xenon gas, Rubidium (as well as other atoms such as nitrogen) are removed from the gas mixture by a freeze-thaw cycle. Pure Xenon gas is then dissolved in the liquid sample of interest (or blown on the solid surface to be studied). Polarization is then transferred via a process known as SPINOE. While high levels of Xenon polarization can be attained, the ultimate nuclear polarization of the target fluid is somewhat small because xenon does not dissolve well enough. Also, the generation of hyperpolarized Xenon is far from trivial, requiring optical excitation, applied magnetic fields, relatively high temperatures (about 450 K), a controlled gas mixture, the removal of Rubidium (which is toxic), etc.
International Patent publication WO2014/165845 uses green light to continuously illuminate nitrogen vacancy (NV) centers and spin relaxation leads to nuclear spin polarization on a diamond surface. The technique disclosed in an article entitled “Recursive Polarization of Nuclear Spins in Diamond at Arbitrary Magnetic Fields” in Applied Physics Letters 105 (Dec. 15, 2014) 242402 demonstrates nitrogen polarization of about 80% at room temperature (e.g. 25° C.±5° C.) and in the presence of only a very small magnetic field. This corresponds to approximately six orders of magnitude higher polarization than that possible with the strongest NMR magnet commercially available today. While the prior technique is useful in some situations, a more general and versatile version of this approach is desirable. The content of WO2014/165845 is hereby incorporated by reference.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.